Hello All:
Short circuit compiler transformation for conditional branches. The conditional
branches based on the conditional
Expressions one of the path is always executed thus short circuiting the path.
Certains values of the conditional
Expressions makes the conditional expressions always true or false. This part
of the conditions in extracted out
In the IF-THEN cond_express with the check of the value and in the else case
the original expressions is checked.
This makes for a given values of the variables of the conditional expressions
makes the conditional expression as
True or false always and the one path is always executed.
For the example given below.
For( x1 = lb1; x1 < = ub1 ; x1++)
{
If ( C1 && C2)
S_then
}
Fig (1).
For the input code given in Fig (1) the condition C1 && C2 is always false if
C1 or C2 is zero(false) thus short circuiting
The path and only s_else will be executed if C1 or C2 is false.
Thus the input code is transformed as follows.
For( x1 = lb1; x1 < = ub1 ; x1++)
{
If(!C1)
Continue
else
S_then
}
This is much simpler code and there could be complex expressions inside the FOR
Loop that can be extracted out with
Different versions of the conditional IF-THEN-ELSE inside the loops based on
short circuiting executing one of the path always
Executed can be extracted in IF-THEN and other cases of condition will be
inside the else conditions.
Again this has to be optimized based on the profile Data of hot conditional
branches and the above optimizations is performed
Based on the hotness of the conditional branches.
The short Circuiting optimization also makes the irreducible loops with
conditional branches as reducible and there is no need for
Conversion of irreducible loops to reducible loop with any of the existing
approach like node splitting for the short circuiting candidate.
This optimizations is implemented in LLVM and I would like to know if this is
implemented in GCC. If not implemented I would like
To propose this short circuit compiler transformation.
Thoughts Please ?
Thanks & Regards
Ajit
